This invention pertains to a rapping hammer system adapted for providing single mechanical impacts on tube units for periodically removing accumulated outside deposits from multiple tubes, such as from boiler tube units, and includes a method for operating the rapping hammer system.
Cleaning of outside surfaces of heat exchanger tubes such as boiler tubes to remove accumulated ash and other deposits has been accomplished by utilizing various tube rapping means or systems. Such rapping systems usually consist of a series of hammers which impact upon a bar or header physically connected to the tubes being cleaned. Such impacting or rapping of the hammers excites tube vibrations, which results in a tube cleaning action for substantially removing deposits accumulated on the tubes. Relatively high input energies are needed for impacting the tube headers to sufficiently excite the tubes and thereby provide an adequate cleaning action. Typical maximum acceleration imposed upon the tube headers are in the range of up to 200 g's, resulting in maximum tube acceleration of 25 g to 100 g's required for proper cleaning, depending upon the type of deposits on the tubes.
The tube rapping procedure is usually performed in several rapping cycles, so that within one cycle several headers located in close proximity and typically parallel to each other are sequentially rapped, say in a sequence of 1, 2, 3, . . . n, etc., where n is the total number of headers and/or impact bars. Each header/impact bar is rapped by one hammer and thus the number of hammers required equals the number of header/collection bars included in a heat exchanger installation. In a typical rapping hammer system, all the hammers are connected to and driven by a common shaft and are spaced apart according to the spacing of the headers. The impacting of the hammers on the headers is typically arranged in distinct time intervals, so that no two hammers will impact upon the headers at the same time for reasons of dynamic interaction effects, which could reduce the cleaning effectiveness of the rapping procedure on the headers. Typical examples of such conventional mechanical rapping hammer systems are disclosed by Tuomaala U.S. Pat. No. 3,835,817 and Gamache et al. U.S. Pat. No. 5,315,966.
In a typical rapping hammer arrangement, the hammers are rotatably attached to a common shaft and when the hammers are rotated into their upper position they will fall and impact upon the header/collection bars by effect of gravity. Typically, the hammer will rotate from a near upright (upper) position to its lowermost vertical position and strike the header horizontally by way of an impact stem which is attached to the header/impact bar. After impacting the hammer, the hammer usually rebounds and immediately strikes the header again, then rebounds and strikes the header again, etc. until the energy of impact is gradually dissipated. The hammer typically impacts the header stem 3, 4 and more times in very short time intervals, before it is rotated away and raised for the next series of impacts on the header. However, because the tube cleaning effect by such rapping of the headers is achieved mainly on the first large or major impact of the hammer against the header, and not by the subsequent repeated smaller or minor impacts which follow and are usually undesirable for effective tube cleaning, improved rapping hammer systems are desired.